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android - “WebView 不能为空”的特殊情况

问题描述

我正在尝试在此代码中通过单击打开第二个活动和链接的按钮来打开网站。

我的第一个活动代码：

package com.medanis.fneclis

import android.content.Intent
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        button1.setOnClickListener{
            val intent = Intent(this, License::class.java)
// To pass any data to another activity
            intent.putExtra("targetURL", "www.firstlink.com")
// start your SecondActivity
            startActivity(intent)

        }
        button2.setOnClickListener{
            val intent = Intent(this, License::class.java)
// To pass any data to another activity
            intent.putExtra("targetURL", "www.secondlink.com")
// start your SecondActivity
            startActivity(intent)

        }
        button3.setOnClickListener{
            val intent = Intent(this, License::class.java)
// To pass any data to another activity
            intent.putExtra("targetURL", "www.thirdlink.com")
// start your SecondActivity
            startActivity(intent)

        }
    }
}

我的第二个活动代码：

package com.medanis.fneclis

import android.content.Intent
import android.os.Build
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.support.annotation.RequiresApi
import android.webkit.ClientCertRequest
import android.webkit.WebResourceRequest
import android.webkit.WebView
import android.webkit.WebViewClient
import kotlinx.android.synthetic.main.activity_license.*
import kotlinx.android.synthetic.main.activity_license.view.*
import java.net.URL

class License : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_license) // replace with you xml file name webview
        var  url : String = intent.getStringExtra("value")?:""
        webv.webViewClient = WebViewClient()
        startActivity(intent)
    }
}

许可证布局：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/bg2"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/fneclis_phone_bg_5"
    android:orientation="vertical"
    android:theme="@style/AppFullScreenTheme"
    tools:context=".License">

    <Button
        android:id="@+id/wvbtn"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:layout_marginEnd="316dp"
        android:layout_marginLeft="18dp"
        android:layout_marginRight="316dp"
        android:layout_marginStart="18dp"
        app:layout_constraintBottom_toTopOf="@+id/webv"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <WebView
        android:id="@+id/webv"
        android:layout_width="0dp"
        android:layout_height="513dp"
        android:layout_marginTop="36dp"
        android:background="@drawable/ic_launcher_background"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintDimensionRatio="w,1:1"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/wvbtn">

    </WebView>

</android.support.constraint.ConstraintLayout>

MAINACTIVITY 布局：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/bg"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/fneclis_phone_bg_3"
    android:orientation="vertical"
    android:theme="@style/AppFullScreenTheme"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button1"
        android:layout_width="263dp"
        android:layout_height="116dp"
        android:layout_marginBottom="25dp"
        android:layout_marginTop="13dp"
        android:background="@drawable/fneclis_btn"
        android:text="Next Page"
        android:textSize="30sp"
        app:layout_constraintBottom_toTopOf="@+id/button3"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.504"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button2" />

    <Button
        android:id="@+id/button3"
        android:layout_width="263dp"
        android:layout_height="116dp"
        android:layout_marginBottom="76dp"
        android:layout_marginTop="400dp"
        android:background="@drawable/fneclis_btn"
        android:text="Next Page"
        android:textSize="30sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.504"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button2"
        android:layout_width="263dp"
        android:layout_height="116dp"
        android:layout_marginBottom="346dp"
        android:layout_marginTop="130dp"
        android:background="@drawable/fneclis_btn"
        android:text="Next Page"
        android:textSize="30sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.504"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0" />

</android.support.constraint.ConstraintLayout>

错误信息：

java.lang.RuntimeException：无法启动活动 ComponentInfo{com.medanis.fneclis/com.medanis.fneclis.License}：java.lang.IllegalStateException：webv 不能为空

标签： androidandroid-studiokotlin

解决方案

实际上你的代码有很多问题，首先是背景，摆脱它。

这就是您的 activity_license.xml 的外观：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/bg2"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:theme="@style/AppFullScreenTheme"
    tools:context=".License">

    <WebView
        android:id="@+id/webv"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent">

    </WebView>

</android.support.constraint.ConstraintLayout>

其次，更改整个许可证活动中的代码，您的 onCreate 必须如下所示：

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_license)
        val url: String = intent.getStringExtra("targetURL") ?: ""
        val webView = findViewById<WebView>(R.id.webv)
        webView.loadUrl(url)
    }

请在您的按钮点击逻辑上添加实际的网址，如下所示：

    button1.setOnClickListener{
        val intent = Intent(this, License::class.java)
        intent.putExtra("targetURL", "https://www.google.com")
        startActivity(intent)

    }

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